Gene Expression

Bryan Caplan notes & argues:

If you take a closer look at BG research, though, you’ll notice something interesting. Virtually every BG study partitions variance into three sources: genes, shared family environment, and non-shared environment. Typical estimates are something like 40-50% for genes, 0-10% for shared family environment, and 50% for non-shared environment.

And what exactly is non-shared environment? Everything other than genes and family environment!

Nevertheless, I strongly suspect that if non-shared environment’s contribution to behavioral variance were a lot smaller, determinists would be heralding the result as “proof” of their position. And if this suspicion is right, it’s only fair to ask them to reduce their confidence in light of the findings of BG research.

This seems about right. The only issue I have is that as Caplan notes there isn’t really a lot of data on what the unaccounted for “non-shared environment” is. If it’s just so much “noise,” there are pretty much no policy implications, right? Whereof one does not know, one must do no harm.

Related: Environment as the gene’s handmaid.


  1. #1 jb
    April 20, 2009

    I was intrigued by Caplan’s comment about believing in Free Will, so I took a look at his essay on the subject:

    WTF? Right up front he denies the Law of Causality, effectively assuming his conclusion. Very unimpressive!

  2. #2 lol
    April 20, 2009

    The effect of non-shared environment can be seen clearly in inbred model organisms. Most are genetically uniform and can be raised in conditions that are close as possible to uniform “shared” environment. Yet you still get lots of phenotypic variance, and this is largely non-shared environment.

  3. #3 Eric J. Johnson
    April 20, 2009

    “Non-shared environment” seems a downright faulty term if it includes things like epistasis and stochastic molecular events.

  4. #4 lol
    April 20, 2009

    if you want to read about free will, skip caplan’s essay and go here:

    for the advanced reader:

    and if you really have to:

  5. #5 Neuroskeptic
    April 20, 2009

    If you want to read about free will read Dan Dennet’s “Freedom Evolves”. It’s awful, which is rather educational, because it will show you how even an otherwise smart guy can tie himself up in knots trying to defend free will.

    As for those genetic determinists – who are they? Is there really anyone left who thinks genes fully & completely determine any behavioural traits?

  6. #6 wybory sondaze demokracja
    April 20, 2009

    As for me genes give possibilities. They are a kind of ‘canvas’ but the ‘pattern’ we choose and create on our own. Genes can be both: opportunity and limitation at the same time, but it depends on us (ok, at the very beginning we need to rely on our parents) how we use them. We can extend our inborn skills or just give them up, but what is the Free Will involved in here for?…

  7. #7 Escuerd
    April 20, 2009

    Neuroskeptic, I was initially going to ask exactly the same thing. I’ve never heard of any high profile genetic determinist.

    But it looks like Caplan is talking about regular determinism (i.e. the whole system, genes+environment is deterministic), not genetic determinism.

    His argument was correct, but a fairly weak point in favor of free will. That is, if we assume that we know what “free will” means and that it’s not deterministic (though Caplan’s attempt at defining it as something neither deterministic nor random makes no sense).

    I wonder how much sensitivity to initial conditions (chaos) there is in the development of brains. If there is a lot (as I would guess), then it would be difficult to ever account for all of the variance in behavior in terms of causal variables, even if it is all causally determined.

  8. #8 Neuroskeptic
    April 22, 2009

    Escuerd: Actually, I think you’re right. I misread Caplan. But so did Razib in the post title 😛

    The argument that behavioural genetics should make plain old determinists reconsider their position is quite interesting. But personally I think the only scientific findings that are relevant to determinism are from physics. Physics trumps behavioural genetics…

    But more fundamentally, I don’t think that the existence of “free will” is an empirical question at all. Free will has nothing to do with determinism because the concept of “free will” is simply not a meaningful one. it’s a fuzzy collection of folk intuitions stuck together with philosophical duct-tape. If you ask me.

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